The transmission type electron microscope which enables the observation of an electron microscope image on a monitor CRT by using a TV camera fitted thereto is known (see Proceedings of the 43rd Annual Meeting of the Electron Microscopy Society of America, 1985; Proceedings of the XIth Congress on Electron Microscopy, Kyoto, 1986, etc.)
According to such a known transmission type electron microscope as mentioned above, a film for photographing the electron microscope image is disposed so that it can be inserted into and removed from an electron beam axis and so that it is positioned below a fluorescent screen for observing the electron microscope image. The fluorescent screen is so disposed that it can be inserted into and removed from the electron beam axis, and moreover, an electron-beam scintilator or illuminant for a TV camera, which is constructed of a fluorescent screen, is disposed below the film. When the fluorescent screen for observing the electron microscope image and the film for photographing the electron microscope image are removed from the electron beam axis, the electron microscope image is formed on the electron-beam illuminant. This projected electron microscope image is picked up by the TV camera and displayed on the monitor CRT.
As is seen from the above, the electron-beam illuminant for the TV camera is disposed below the fluorescent screen for observing the electron microscope image and the film for photographing the electron microscope image. Consequently, extraneous matters (chips, dust and the like), which happen to be produced when both the fluorescent screen and the film are inserted into and removed from the electron beam axis, drop onto the electron-beam illuminant and become a hindrance to observation of a TV image. Being located invariably in the same positions, in addition, these extraneous matters are deposited with the passage of time and thus increase steadily, and therefore said hindrance is increased with the passage of time.
Such a hindrance can be eliminated by cleaning the electron-beam illuminant for the TV camera. However, it is necessary to break the vacuum of the tube of the electron microscope for this cleaning, and accordingly much time and labor are needed therefor. Disclosure of Invention
One object of the present invention is to furnish a transmission type electron microscope which is suited for observing an electron microscope image as a TV image.
Another object of the present invention is to furnish a transmission type electron microscope which is suited for preventing the drop of extraneous matters onto the electron-beam illuminant for a TV camera.
Still another object of the present invention is to furnish a transmission type electron microscope which is suited for increasing the brightness of an image formed on the electron-beam illuminant for a TV camera.
Yet another object of the present invention is to furnish a transmission type electron microscope which is suited for reducing the damage of a sample due to electron beams.
According to the present invention, a transmission type electron microscope is furnished which is equipped with a means to generate an electron beam; a means to irradiate a sample with the electron beam; a means to form at a predetermined position an image of the electron beam which is transmitted through said sample irradiated with the aforesaid electron beam; a means disposed at the predetermined position to transform said image of said electron beam into a visible image; an electron-beam illuminant; a means to position said electron-beam illuminant selectively at a first position whereat it is exposed to the aforesaid electron beam proceeding from the aforesaid electron beam image forming means to the aforesaid visible image transformation means, and at a second position whereat it gets out of the exposure, the aforesaid electron-beam illuminant transforming an electron beam image formed thereon into a light image when said electron-beam illuminant is positioned at the aforesaid first position; a TV camera to pick up the light image; and a means to display the image picked up.